1. Field of the Invention
The present invention is generally related to a control system for an internal combustion engine and, more specifically, to a control system that is capable of determining the air charge mass for the internal combustion engine based on input from sensors that provide barometric pressure, manifold temperature, throttle position, and engine speed.
2. Description of the Prior Art
Many different types of internal combustion engines are well known to those skilled in the art. In those internal combustion engines which provide an engine control unit (ECU) which monitors various parameters and controls the operation of the engine, it is often necessary to determine the air charge mass in the combustion chambers of the engine during each ignition event. This information is often used by the engine control unit (ECU) to determine an appropriate throttle position and/or fuel injection amount to achieve a desired engine output.
U.S. Pat. No. 5,282,449, which issued to Takahashi et al on Feb. 1, 1994, describes a method and system for engine control. To ensure a high precision simultaneous control of the engine generated torque, air fuel ratio of the automobile engine and related factor, the present invention calculates the target air mass flow rate as the air mass flow rate at the inlet port which achieves the target torque, estimates the air flow condition inside the intake manifold, supplies the result to the fuel injection control system and the throttle control system and determines the fuel injection pulse width which achieves the target air fuel ratio according to the estimated air mass flow rate at the inlet port for the fuel injection control system, while determining the throttle angle which achieves the target torque according to the estimated condition and the target air mass flow rate for the throttle control system.
U.S. Pat. No. 5,331,936, which issued to Messih et al on Jul. 26, 1994, describes a method and apparatus for inferring the actual air charge in an internal combustion engine during transient conditions. A mass air flow based control system for an internal combustion engine is provided which is capable of inferring cylinder air charge during non-steady state periods of operation of the engine. The control system infers cylinder air charge from values of rotational engine speed, air mass flow inducted into the engine, inlet air temperature, engine coolant temperature, and barometric pressure. The control system employs the inferred cylinder air charge value for air/fuel ratio control.
U.S. Pat. No. 5,497,329, which issued to Tang on Mar. 5, 1996, describes a prediction method for engine mass air flow per cylinder. A delta model is used to calculate a predicted manifold absolute pressure (MAP) for a future period and the air mass induced in each cylinder is calculated from such a predicted value and used to determine the correct amount of fuel to inject at that period. Several reference pulses generated for each crankshaft revolution establish one or more sets of equally-spaced points at which measurements are made of the parameters MAP, throttle position, exhaust gas recirculation value, and idle air control. A base value of MAP is calculated, trends of changes in the parameters are calculated for each set of points, and weighted values of the trends are summed with the base value to predict a value of MAP. Alternatively, mass air flow (MAF) is measured as well as the other parameters and mass air per cylinder (MAC) is calculated. Then a base value of MAC is calculated, trends of changes in the parameters are calculated for each set of points, and weighted values of the trends are summed with the base value to predict a value of mass air induced into a cylinder.
U.S. Pat. No. 5,889,204, which issued to Scherer et al on Mar. 30, 1999, describes a device for determining the engine load for an internal combustion engine. The invention provides a device for determining the engine load for an internal combustion engine, such device having an input channel for receiving an item of engine speed information, as well as an intake manifold pressure sensor, and an air mass flow rate sensor arranged upstream of a throttle valve, and/or a throttle valve angle sensor. The engine speed is fed to a Kalman filter as an input value and at least one of the three variables, including intake manifold pressure, throttle valve air mass flow rate, and throttle valve angle, is fed as a variable measured by the respective sensor. The Kalman filter derives estimated values for the variables intake manifold pressure and throttle valve air mass flow rate, with which the air mass flowing into a respective cylinder of the engine per working cycle is determined.
U.S. Pat. No. 6,098,602, which issued to Martin et al on Aug. 8, 2000, describes an exhaust gas recirculation system. The EGR system for an internal combustion engine comprises a stepper motor driven EGR valve to control the rate of exhaust gas recirculation in the engine and an electronic controller for determining a desired EGR percent mass flow rate as a function comprising a rotational speed value and an air charge value of the engine, converting the EGR percent mass flow rate to an EGR mass flow rate value, adjusting the EGR mass flow rate value as a function of an exhaust gas temperature value and an absolute exhaust gas back pressure value using MAP values, determining a pressure ratio value across an EGR orifice cooperating with the EGR valve, and determining a required number of motor steps as a function of the adjusted EGR mass flow rate value and the pressure ratio value to achieve the desired EGR percent mass flow rate.
U.S. Pat. No. 6,115,664, which issued to Cullen et al on Sep. 5, 2000, describes a method of estimating engine charge. The method of estimating the total charge to cylinders of an internal combustion engine where the total charge comprises the sum of the air charge and the EGR charge is provided. The total charge is estimated by determining a linear total charge versus MAP reference function at selected engine speeds and at a preselected reference barometric pressure, reference engine coolant temperature, and reference manifold air charge temperature and determining a current barometric pressure value, a current engine coolant temperature value, and a current intake manifold air charge temperature. An intercept of the total charge versus MAP reference function with a total charge axis is adjusted for current barometric pressure different from the reference barometric pressure, and the slope of the total air charge versus MAP reference function is adjusted for current engine coolant temperature and current manifold air charge temperature different from the reference engine coolant temperature value and the reference manifold air charge temperature value. An adjusted total charge is determined by engine control logic based on the adjusted intercept and the adjusted slope of the engine. An estimated EGR charge can be subtracted from the adjusted total charge to estimate air mass flow rate entering the engine cylinders.
U.S. Pat. No. 6,125,830, which issued to Kotwicki et al on Oct. 3, 2000, describes a flow measurement and control system with estimated manifold pressure. An exhaust gas recirculation system directs exhaust gasses from an exhaust manifold to an intake manifold of an internal combustion engine. The exhaust gasses travel from the exhaust manifold, first passing through a flow control valve and then through a measuring orifice before entering the intake manifold. Pressure difference across the orifice is used, along with estimated manifold pressure from a mass air flow sensor, to measure and control exhaust gas flow.
U.S. Pat. No. 4,999,781, which issued to Holl et al on Mar. 12, 1991, describes a closed loop mass airflow determination via throttle position. Mass air flow into an internal combustion engine is measured as a function of throttle opening. The mass air flow rate is expressed as an idle offset constant and the product of gain and effective air intake area which is a function of throttle position. During idle, the idle offset term is updated in response to an exhaust oxygen sensor feedback and during part throttle operation the gain is similarly updated to achieve stoichiometry. For subsonic air flow the mass air flow is further modified as a function of the ratio of manifold pressure to the pressure upstream of the throttle. At the same time the manifold dilution is controlled via an EGR valve to a predetermined schedule.
U.S. Pat. No. 5,771,866, which issued to Staerzl on Jun. 30, 1998, discloses a nozzle for a low pressure fuel injection system. A nozzle is provided for a fuel injection system in which a cap is disposed around a common termination of a first and second conduit. The first and second conduits are associated in coaxial and concentric relation with each other. A liquid fuel is transmitted through the first conduit and air is transmitted through the second conduit. The air is taken into the second conduit at atmospheric pressure without the need for an air compressor. An opening is formed at the cap of the nozzle to allow the fine mist formed at the common termination of the first and second conduits to flow out of the nozzle and into the air stream, such as within an intake manifold, for transport in the air stream to the combustion chamber of a cylinder within the internal combustion engine.
U.S. Pat. No. 5,988,139, which issued to Wasilewski et al on Nov. 23, 1999, discloses a method and apparatus for controlling an internal combustion engine. An engine control system digitally stores corresponding values of timing angles and engine speeds and selects the timing angles based on the operating speed of the engine. At the engine speed range near idle speed, the timing angle is set to a preselected angle after top dead center (ATDC) and the relationship between engine speed and timing angle calls for the timing angle to be advanced from the preselected angle after top dead center (ATDC) to successively advancing angles which subsequently increase angles before top dead center (BTDC) as the engine increases in speed. In one application, a timing angle of 10 degrees after to dead center (ATDC) is selected for an engine idle speed of approximately 800 RPM. This relationship, which is controlled by the engine control unit, avoids stalling the engine when an operator suddenly decreases the engine speed.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
As can be seen in the above described patents, many different control systems require knowledge of the air charge mass within the combustion chamber of the cylinders of the engine. The magnitude of the charged air mass can be determined in several ways. One way that is known to those skilled in the art is to provide a mass air flow sensor (MAFS) that directly reads the mass air flow passing through the air intake passage of the engine. The mass air flow sensor can comprise a small thermal detector and heaters supported on a very small silicon bridge or, alternatively, can comprise a hot wire anemometer. Another method for determining the mass air flow into an engine uses a manifold absolute pressure (MAP) sensor in combination with a charge air temperature sensor.
Sensing mass air flow or manifold absolute pressure within the air intake manifold requires a certain degree of flow stability within the manifold. Rapid changes in pressure and flow rate within the intake passage of an engine cause severe problems if the sensors are intended to provide reliable steady state magnitudes of the monitored parameters. This is particularly exacerbated in engines which have small air intake passages with little volume. In other words, very short air intake manifolds typically do not contain enough volume to act as an accumulation to damp or smooth the rapidly changing pressures caused by the opening and closing of intake valves of the engine. As a result, the reliability of pressure measurements or air flow measurements provided by sensors within the air intake manifold is significantly decreased. It would therefore be significantly beneficial if a system could be provided for determining the air charge mass for an internal combustion engine without having to measure manifold absolute pressure or mass air flow within the air stream passing through the air intake manifold.
A method for determining the air charge mass for an internal combustion engine, in a preferred embodiment of the present invention, comprises the steps of measuring the barometric pressure proximate the engine, measuring the temperature of air proximate an air intake passage of the engine, and determining a position of a throttle of the engine. In addition, it comprises the step of calculating the air charge mass as a function of the barometric pressure, the temperature of air flowing into the air intake passage of the engine, and the position of the throttle of the engine.
The barometric pressure can be measured at any location reasonably proximate the engine since barometric pressure is a function of the environment and does not change rapidly. In addition, the temperature of the air proximate the air intake passage can be measured either within the air intake manifold or proximate the intake passage. The throttle position can be determined by a rotational position sensor or, when a stepper motor is used to position the throttle plate, from signals taken directly from the stepper motor or provided to the stepper motor as position commands.
The method of the present invention can further comprise a step of determining an actual exposed area of the throttle body passage as a function of the position of the throttle of the engine and determining a throttle effective area by adjusting the actual exposed area by a non-isentropic flow factor.
In a preferred embodiment of the present invention, the method can further comprise the step of determining the effective throttle area directly from the position of the throttle of the engine.
The present invention can further comprise the step of selecting a predetermined ratio of manifold pressure to barometric pressure as a dual function of an operating speed of the engine and a value which is calculated as a function of cylinder swept volume, number of cylinders, engine speed, the ideal gas constant, manifold air temperature, and throttle effective area.